1. Field of the Invention
The present invention relates to a positive resist composition suitable for use in the ultramicrolithography process such as production of VLSI or a high-capacity microchip or in other photofabrication processes. More specifically, the present invention relates to a positive resist composition capable of forming a high-resolution pattern by using KrF excimer laser light, electron beam, EUV light or the like, that is, a positive resist composition suitably usable for fine processing of a semiconductor device, where KrF excimer laser light, electron beam or EUV light is used, and a pattern forming method using the composition.
2. Description of the Related Art
In the process of producing a semiconductor device such as IC and LSI, fine processing by lithography using a photoresist composition has been conventionally performed. Recently, the integration degree of an integrated circuit is becoming higher and formation of an ultrafine pattern in the sub-micron or quarter-micron region is required. To cope with this requirement, the exposure wavelength also tends to become shorter, for example, from g line to i line or further to KrF excimer laser light. At present, other than the excimer laser light, development of lithography using electron beam, X ray or EUV light is proceeding.
The lithography using electron beam or EUV light is positioned as a next-generation or next-next-generation pattern formation technique and a high-sensitivity and high-resolution positive resist is being demanded. Particularly, in order to shorten the wafer processing time, the elevation of sensitivity is very important, but in the positive resist for electron beam or EUV, when higher sensitivity is sought for, not only reduction in the resolving power but also worsening of the defocus latitude depended on line pitch are incurred and development of a resist satisfying these properties at the same time is strongly demanded. The defocus latitude depended on line pitch as used herein means a difference in the pattern dimension between a high density portion and a low density portion of a resist pattern and when this difference is large, the process margin is disadvantageously narrowed at the actual pattern formation. How to reduce this difference is one of important problems to be solved in the resist technology development. The high sensitivity is in a trade-off relationship with high resolution, good pattern profile and good defocus latitude depended on line pitch and it is very important how to satisfy these properties at the same time.
Furthermore, also in the lithography using KrF excimer laser light, how to satisfy all of high sensitivity, high resolution, good pattern profile and good defocus latitude depended on line pitch is an important problem, and this problem needs to be solved.
As for the resist suitable for such a lithography process using KrF excimer laser light, electron beam or EUV light, a chemical amplification-type resist utilizing an acid catalytic reaction is mainly used from the standpoint of elevating the sensitivity and in the case of a positive resist, a chemical amplification-type resist composition mainly comprising an acid generator and a phenolic polymer which is insoluble or sparingly soluble in an alkali developer but becomes soluble in an alkali developer under the action of an acid (hereinafter simply referred to as a “phenolic acid-decomposable resin”), is being effectively used.
With respect to such a positive resist, there are known some resist compositions using a phenolic acid-decomposable resin obtained by copolymerizing an acid-decomposable acrylate monomer having an alicyclic group as the acid-decomposable group. Examples thereof include the positive resist compositions disclosed in U.S. Pat. No. 5,561,194, JP-A-2001-166474 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-2001-166478, JP-A-2003-107708 and JP-A-2001-194792.
In U.S. Pat. No. 6,312,870, a resist comprising a resin containing a repeating unit derived from a cinnamic acid ester is disclosed with an attempt to improve the pattern profile and the etching resistance.
In JP-A-7-234511, a chemical amplification-type resist using a resin having a hydroxystyrene and a benzyl ester is disclosed.
However, by any combination of these techniques, it is impossible at present in the ultrafine region to satisfy all of high sensitivity, line width roughness and good defocus latitude depended on line pitch.